docs: def handle_date(self, value):
          """
          Attempt to coerced date to ISO8601.
          """
          try:
              return iso8601.parse_date(unicode(value)).year
          except iso8601.ParseError:
              for datefmt in ("%B %d, %Y", "%Y-%m", "%Y-%m-%d", "%m/%d/%Y"):
                  try:
                      # TODO: remove str coercion.
                      return datetime.strptime(unicode(value), datefmt).date().year
                  except ValueError:
                      pass